With mixer on medium-high speed, beat butter, brown sugar, cinnamon, nutmeg and salt until creamy. Beat in egg and vanilla. With mixer on low speed, beat in flour until just combined. Transfer to prepared pan. With lightly floured hands, spread into even layer.

Press dough into prepared pan in very thin, even layer. Sprinkle with pistachios; press nuts into dough. With pizza cutter or very sharp knife, cut dough lengthwise into 3-inch-wide rectangles, then crosswise to form 3-inch squares. Cut squares diagonally into triangles.

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